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The 5-AMPase activity of the ectoenzyme 5-nucleotidase has been measured in a variety of cell lines, using intact cells. Human cell types showed two orders of magnitude higher enzyme activity than mouse cell lines. The ectoenzyme is inhibited by adenosine 5-(alpha, beta-methylene) diphosphate and Concanavalin A. A different extent of 5-nucleotidase lectin inhibition was observed in the studied cell lines, suggesting that the corresponding ectoenzymes are glycoproteins with a different type or degree, or both, of glycosylation. The 5-nucleotidase activity increased during subculture and decreased after cell transformation. Generally, the 5-nucleotidase activity was two- to five-fold higher in monolayer than in suspension cell culture. A relation between cell growth and 5-AMPase activity was also observed. Enzyme activity increased at the end of the lag phase (glioblastoma cells) or during the exponential phase (the other two cell lines). After confluence, the activity decreased to the initial or even lower range of activity. Observed activity variations with cell proliferation correlate with modifications of 5-AMPase activity during subculture.

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